Humoral immune response in melanoma and glioma patients: A solubilized melanoma—membrane component as a tool for detecting circulating antibodies

Abstract

In search of tumor-associated components in human melanomas and gliomas, plasma membranes were isolated from these tumors and compared morphologically, biochemically and immunologically with those from normal human brain. The preparations exhibited a comparable ultrastructure of empty vesicles of various form and size. The melanoma membrane consisted of at least 15 protein components and the glioma membrane consisted of at least 24 protein components, four of which were absent in the membrane of normal tissue, as revealed by polyacrylamide gel electrophoresis. The four tumor-associated polypeptides could be solubilized together with a few other membrane components by the non-ionic detergent Triton-X100 and were used as an antigen source for immunologic characterization of melanoma and glioma membranes. A rabbit antiserum prepared against these solubilized membrane components from melanoma were absorbed with plasma membranes from a variety of normal tissue including erythrocytes, lymphocytes, spleen, liver, lung, kidney, placenta and brain. The absorbed antiserum reacted with the membrane extract of all the 11 melanomas tested so far; in addition it cross-reacted with an identically prepared extract from all the 15 gliomas tested. Membrane extracts from other tumors, such as kidney and mammary carcinoma, were negative in this respect. Furthermore, a rabbit antiserum prepared against Triton extract from glioma membranes yielded after exhaustive absorption an immune precipitate not only with the specimens from the 15 other gliomas but also with those from the 11 melanomas. Electrophoretic analysis of the immune precipitate formed by the immunoglobulin fraction of the absorbed rabbit antiserum and the Triton-X100 extract from melanoma membranes exhibited six polypeptide bands, two of which appear antigen-derived as they were missing in the profile of the immunoglobulin pattern. A comparable electrophoretic pattern was obtained with the immune precipitate of the glioma antigen specimen. The molecular weight of these two polypeptides was estimated on the basis of their electrophoretic mobility to be 55,000 and 10,000 daltons, respectively. The electrophoretic immunologic findings argue for a common membrane component in human melanoma and glioma patients. Using the Triton extract from melanoma membranes as an antigen source, precipitating antibodies could be detected in the immunoglobulin fraction of 16 of the 24 sera from melanoma patients and in that of 15 of the 23 glioma patients by means of counter-current electrophoresis. Sera from a variety of cancer patients with diseases other than melanoma or glioma as well as from patients without cancer were negative in this respect.